DISSECTION OF THE NECK. 65 



ures in man), but occasionally the posterior ends are 

 connected by a slender band or isthmus passing across 

 the trachea. 



7. The Mylo-hyoid Muscle lies anterior to the hyoid 

 bone, between the rami of the mandible. It is a 

 thin muscular sheet which arises from the hyoid bone 

 on each side, and is inserted along the inner side of 

 the mandible ; it meets its fellow in the mid-line and 

 forms the floor of the mouth. 



8. The Digastric Muscle is the thick muscle cover- 

 ing the angle and part of the body of the mandible. 

 It arises from the occipital bone of the skull, and is 

 inserted into the mandible, serving to depress the 

 jaw. In the dog it is not truly a digastric muscle, 

 though a tendinous line may be observed running 

 across its belly somewhat posterior to the middle. 



9. The Vago-sympathetic Nerve. The combined 

 trunk of the vagus and sympathetic nerves lies along 

 the trachea on each side, in the same sheath with the 

 carotid artery and internal jugular vein. Expose it 

 on the left side at the middle of the neck; and dis- 

 sect it anteriorly. To expose its origin from the 

 skull, cut the digastric muscle at its mandibular inser- 

 tion and reflect it backward. When the parts are a 

 little more dissected it will be well to remove this 

 muscle entirely, taking .care not to cut the hypoglossal 

 nerve. 



10. The Superior Laryngeal Nerve is a branch of 

 the vagus ; it arises far forward, somewhat beyond the 

 anterior end of the larynx. At its origin from the 

 vagus there is an enlargement of that nerve known as 

 the ganglion of the trunk of the vagus. Trace the 

 superior laryngeal to the larynx, which it enters and 

 supplies with sensory fibres, giving also motor fibres to 



